1. Field of the Invention
The present invention relates to a fuel shut-off valve, which shuts off fuel from flowing out of discharge port for discharging gases that generate in the fuel tank of vehicle.
2. Description of the Related Art
Within a fuel tank, a fuel shut-off valve has been disposed usually. The fuel shut-off valve not only discharges gases that generate resulting from evaporating fuel, but also shuts off the fuel from flowing out of the discharge port. As one of such fuel shut-off valves, a conventional fuel shut-off valve has been know that comprises a casing, a float, and an upper valve element. The casing is installed on the top of fuel tank, and has a top being provided with a connector passage, which is connected to outside canister. The float is accommodated within the valve chamber that the casing forms within itself, and is exerted to increasing and decreasing buoyant force depending on liquid level within the valve chamber, thereby ascending and descending within the valve chamber. The upper valve element is placed on the top of the float. As the liquid level within the fuel tank ascends, enlarging buoyant force is exerted to the float so that the float and upper valve element ascend to close the connector passage. Thus, the conventional fuel shut-off valve keeps fuel from flowing out to the outside of fuel tank.
It has been required that such a fuel shut-off valve demonstrate high sealability at the sealing portion between the float and/or upper valve element and the connector passage even when the sealing portion is soaked in fuel upon driving vehicle in inclined manner. Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2000-130,271 and Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2002-235,623 have been known to disclose techniques that cope with the requirement. For example, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2000-130,271 discloses that a ring-shaped seat member, which is provided with a connector bore and which is made of rubber, is disposed on the upper valve element, and that the ring-shaped seat member's upper seating portion is opened and closed with respect to the connector passage's sealing portion, thereby opening and closing the connector bore and/or the connector passage. Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2000-130,271 discloses that the ring-shaped seat member's lower leading end is formed as a lip shape, and that the float's upper sealing portion opens and closes the ring-shaped seat member's lip-shaped lower leading end, thereby opening and closing the connector bore and/or the connector passage.
However, since the root of the lip-shaped portion, which is formed at the rubber ring-shaped seat member's lower leading end, turns into a thick base, the lip-shaped portion is less likely to flex. Accordingly, the ring-shaped seat member, which Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2000-130,271 discloses, exhibits lower sealability with respect to the float's upper sealing portion. In view of this, it is possible to think of making the lip-shaped portion itself thinner. However, if such is the case, the lip-shaped portion exhibits weakened strength. Consequently, the lip-shaped portion has exhibited degraded durability.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2002-235,623 discloses a seat member whose top and bottom makes a seating portion and a lip-shaped portion, respectively. The seating portion and lip-shaped portion are sealed or opened with respect to the sealing portions of the casing and float, the mating members, respectively. Accordingly, the inner-periphery-side protrusion of the upper valve element's valve body is held between the seat member's base and holding portion, which is disposed below the seat member's seating portion, and thereby the seat member is simply retained to the valve body. Consequently, the pressing force that the float exerts to the seat member's lip-shaped portion has been exerted to the entire seat member to deform the seat member's base end and eventually deform the seat member's base. Therefore, there might arise such a fear that the seat member has come off from the upper valve element's valve body.
Moreover, as it is apparent from Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2002-235,623, the seat member's lip-shaped portion receives upward pressing force from the float when the float seat on the seat member's lip-shaped portion. The upward pressing force is transmitted to the seating portion, with which the seat member is provided on the top of the base. Accordingly, the upward pressing force might impair the flatness of the seat member's seating portion. Consequently, the upward pressing force might adversely affect the sealability between the seat member's seating portion and the casing's sealing portion eventually.